1. Field of the Invention
The present invention relates in general to computers, and more particularly to methods, computer systems, and computer program products for determining the access sequence of data stored on a tape medium.
2. Description of the Related Art
As technology develops, the storage capacity of tape media (e.g., tape drive) continues to grow. Recent advances have led to some tape media having a capacity of 1.5 terabytes (TB). With this increased tape media capacity, tape media may be used in a wide range of applications, from traditional data backup and archiving to file systems.
Tape media, such as tape drives, compare favorably with hard disks in terms of capacity and transfer rate, but finding data dispersed on tape media, which may reach lengths of several hundreds of meters, often requires minutes of data seek time. Drive seek time has long been considered an important issue, and many methods for reducing seek time for various forms of data have been proposed.
In order to be viable for some modern applications, tape drives may need to be able to consecutively read multiple files or logical volumes (e.g., record groups), a process often referred to as “defrag” or “reclamation.” This poses the new challenge of reducing total seek time when accessing multiple record groups in succession. One potential way of reducing total seek time while still maintaining shortened seek times for isolated seek operations is to modify the access sequence for the record groups. Using this method to reduce total seek time depends heavily on a variety of conditions that are unique to tape drives, including the speed and acceleration at which the tape drive moves the tape media, as well as total data band transport time, which makes access sequence modification ideal for tape drives. In order to modify the access sequence on a tape drive and minimize the amount of processing time required for modification, an algorithm with a low computational complexity is required.
Additionally, when the transfer rate between the host and the tape drive is slower than that between the tape drive and tape media, a bottleneck occurs in the tape drive during seek operations and on the host side during read operations. Conventional tape drives begin seek operations after receiving a seek request from the host, which issues the seek request after reading a series of data. In such a system, the tape drive read command itself does not specify position information, relying instead on the seek command for assistance, which makes it problematic to change the order of the seek and read commands. Thus, after the tape drive reads the data requested by the host from the tape media into tape drive memory, the tape media remains idle until the host finishes reading the data.